1. Good for WHAT? I have one and it does everyting I need it to do, but then again the most "stressing" game I have is Guild Wars or Viva Pinata. 2. For some applications it's already behind the curve. 3. ". . . is it changeable?" If by "changeable" you mean upgradeable, no it isn't.
Depends on the laptop, most laptops with good video do have replacable video. It is a great card for CAD & games...it is not super-high end, but it is probably more than the laptop has use for.